Brandts voles have an annual cycle of body weight and adiposity changes,which can be induced in the laboratory by manipulation of the photoperiod.We suggest that voles have evolved mechanisms to cope with the negative sequalae of the obese state through millions of years of evolution.When aged 5 weeks,male Brandts voles were transferred from Long day (16L∶8D,LD) to Short Day (8L∶16D,SD) .After SD acclimation for 10 weeks,the voles were randomly separated into LD (n=19) and SD (n=18) groups and then exposed to these conditions for another 10 weeks.We quantified glucose tolerance and insulin sensitivity (GTT and ITT) ,body composition and organ fat content at the end of the different photoperiod exposures.LD voles exhibited greater white fat pad mass than SD voles (7.1 g VS 3.8 g,p=0.003) ,but their GTT and ITT responses remain the same as SD animals.Fat content in both liver and muscle showed no difference between LD and SD animals.In conclusion,Natural obesity in the Brandts vole is independent of glucose tolerance.This healthy obesity is accompanied with no effect of obesity on fat content of both liver and muscle,supporting the lipotoxicity hypothesis.